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Thread: 4" Main To 1 1/2" Vent

  1. #1
    DIY Junior Member lugnuts's Avatar
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    Default 4" Main To 1 1/2" Vent

    Thanks to everyone who contributes to this awesome resource!

    I'm rebuilding a rotten 2" cast iron kitchen waste stack. It was vented to the roof by a 1 1/2" lead pipe, but everything from the sink trap down to the building main needs replacement. It connected to the building main (4" cast iron) below the basement floor; at this intersection is a 3" floor drain for the basement; there are two water heaters, a washing machine, and a boiler nearby.

    The vertical stack for the bathroom is about 5 feet upstream of this location, and the street is about 15 feet downstream.

    I'd appreciate advice on the proper sequence of fittings from the 4" main below the basement floor up to the 1 1/2" kitchen vent. In between, there is a 3" basement floor drain, a 2" inlet for the washing machine, and a 2" inlet for a kitchen sink + dishwasher

    This is the sequence I'm thinking of, starting at the main and going up:

    Below basement floor
    1. 4" wye + 45 degrees to vertical
    2. San-tee inlet for 3" floor drain

    Above basement floor
    3. 4" cleanout
    4. San-tee inlet for 2" washing machine
    5. Transition to 2"
    6. San-tee inlet for 2" kitchen sink w/dishwasher
    7. Transition to 1 1/2" vent

    I'm concerned that a 4" pipe rising from the basement floor and then transitioning to 2" just won't look right or be correct. I appreciate everyone's advice. Thanks!

    Will

  2. #2
    Moderator & Master Plumber hj's Avatar
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    Without actually being there, we cannot make an assessment based on your description. IF that 4" is the only 4" riser from the floor, then it does need a 4" cleanout opening, but from that point you can reduce it down to the proper sizes for the other openings.
    Licensed residential and commercial plumber

  3. #3
    DIY Junior Member lugnuts's Avatar
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    Thanks for your response, HJ!

    I've attached a diagram of the project; I appreciate any guidance you may have on where to make transitions in the area shown in green.

    This location is downstream of the bathroom stack, which has a 4" vent all the way to the roof, so the 1 1/2" vent for this riser would be an auxiliary vent.

    Thanks!
    Will

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  4. #4
    Moderator & Master Plumber hj's Avatar
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    The floor drain and washing machine will not be vented, and you cannot use those "sweep" fittings for any of the three connections.
    Licensed residential and commercial plumber

  5. #5
    Retired Defense Industry Engineer jadnashua's Avatar
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    A line can be either a vent or a drain, it cannot be both! To vent the WM, you'd need to run a second line vertically and connect it at least 42" above the floor, or 6" above the flood plane of the highest fixture using the drain, whichever is higher.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  6. #6
    DIY Junior Member lugnuts's Avatar
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    Thanks for the responses!

    jadnashua - you're right. I would be wet venting the washing machine. I can run a separate vent for the WM that joins the VTR 6" above the flood rim of the kitchen sink.

    HJ - my drawing is poor; all the inlets are san-tees. Thanks!

  7. #7
    Retired Defense Industry Engineer jadnashua's Avatar
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    Drain connections should normally be Y's (and a 45), a santitary T generally, in the vent (I think I got that right!).
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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